The present invention relates to an aluminum alloy or aluminum alloy material with good cuttability (machinability).
The present invention also relates to a method for producing a forged article using the alloy or alloy material.
The present invention also relates to a forged article obtained by the method above.
Conventionally, aluminum-based alloys prepared by adding Pb, such as JIS 2011 alloy and JIS 6262 alloy, have been used as aluminum alloys with good cuttability.
However, aluminum alloys having good cuttability without adding Pb have been required in recent years, in light of environmental problems.
While aluminum-based alloys prepared by adding Sn and Bi have been proposed as substitutes for the JIS 2011 alloy (prepared by adding Pb and Bi), their chip splittability is often inferior to the alloys prepared by adding Pb and Bi. In addition, chip splittability is insufficient when the rotation speed of the material is reduced or feed speed of the blade is slowed to comply with the requirement to reduce the surface roughness of the articles, compared with those conventionally made.
Further, when the alloy material prepared by adding Sn is subjected to hot-forging, cracks that are not found in the conventional alloys prepared by adding Pb and Bi are occurred in some cases in water-quenching after solution heat treatment carried out after forging.
The present invention is an aluminum alloy with good cuttability, which comprises 3 to 6 mass % of Cu, 0.2 to 1.2 mass % of Sn, 0.3 to 1.5 mass % of Bi, and 0.5 to 1.0 mass % of Zn, with the balance being aluminum and inevitable impurities.
Further, the present invention is a method for producing a forged article, which comprises the step of: forging the above aluminum alloy, at a forging temperature of a material to be forged of 320 to 450xc2x0 C.
Further, the present invention is a forged article obtained by the above producing method.
Other and further features and advantages of the invention will appear more fully from the following description.
According to the present invention, there are provided the following means:
(1) An aluminum alloy with good cuttability, comprising 3 to 6 mass % of Cu, 0.2 to 1.2 mass % of Sn, 0.3 to 1.5 mass % of Bi, and 0.5 to 1.0 mass % of Zn, with the balance being aluminum and inevitable impurities;
(2) A method for producing a forged article, comprising the step of: forging the aluminum alloy according to item (1), at a forging temperature of a material to be forged of 320 to 450xc2x0 C.; and
(3) A forged article, obtained by the method according to item (2).
The phrase xe2x80x9cPb is not added (not supplemented with)xe2x80x9d as used herein means that no Pb is added in the ingot, and more specifically it means 0.05 mass % or less of content of Pb in the resulting aluminum alloy.
The present invention will be described in detail hereinafter.
Cu contributes to improving mechanical strength of the aluminum alloy of the present invention, by forming a compound, such as CuAl2. The effect is small in the range below the lower limit of the content of Cu, and the quality of the surface of the ingot decreases in the range above the upper limit of the content of Cu. The preferable content of Cu is 4.5 to 5.5 mass %.
Low-melting-point elements, such as Sn and Bi, improve chip splittability. Since Sn and Bi form almost no solid solution with aluminum, they exist as compounds. It is assumed that chip splittability is improved because the compounds melt at the tip of a cutting or drilling blade due to heat in working, to generate notches on the chips. This effect is insufficient at below the lower limits of the contents of Sn and Bi, and corrosion resistance decreases above the upper limit contents, due to occurrence of grain boundary corrosion. Since the melting point of the Snxe2x80x94Bi compound decreases to 139xc2x0 C., in contrast to the melting points of pure Sn of 232xc2x0 C. and pure Bi of 271xc2x0 C., the effect of melting of the compound becomes evident. Accordingly, adding both Sn and Bi is preferable, and they are preferably contained in an Sn-to-Bi mass ratio of about 43:57, which causes a eutectic composition. The content of Sn is preferably 0.2 to 0.8 mass %. The content of Bi is preferably 0.3 to 1.0 mass %.
Hitherto, chip splittability of the aluminum-based alloy material prepared by adding Sn and Bi has been inferior to that of the material prepared by adding Pb and Bi in some cases. The present inventors found the reason to be as follows, as a result of intensive studies. Since the Snxe2x80x94Bi compound has a smaller size than the Pbxe2x80x94Bi compound, notches having a size sufficient to split the chips cannot be formed, in some cases of specific cutting conditions.
Accordingly, the present inventors have found that Zn is to be added, with addition of Bi in a content of 0.3 mass % or more, to increase the size of the compound. That is, it has been found that the size of the Snxe2x80x94Bi compound increases by introducing Zn into the Snxe2x80x94Bi compound. For example, in the example described later, the average grain diameter of the Snxe2x80x94Bi compound became as large as 8 xcexcm in Sample 2 according to the present invention, in contrast to the average grain diameter of 5 xcexcm of the Snxe2x80x94Bi compound in Sample 9 of a comparative example. This shows that the size of the Snxe2x80x94Bi compound in the sample according to the present invention was almost equal to that of the Pbxe2x80x94Bi compound in JIS 2011 alloy as a conventional example. Consequently, notches having sufficient size are formed, to improve chip splittability. The average grain diameter of the Snxe2x80x94Bi compound is preferably 8 xcexcm or above, more preferably 10 xcexcm or above. The above effect is insufficient at a Zn content of below the lower limit, and corrosion resistance is deteriorated at a content above the upper limit. The Zn content is preferably 0.5 to 0.8 mass %.
Other elements are not particularly restricted in the alloy of the present invention. Elements like Si, Fe, Mn, Mg, Ti, Ni, Cr, Zr, and In may be contained, in ranges not inhibiting the various properties of the alloy of the present invention, such as mechanical strength, moldability, cuttability, and corrosion resistance.
The manufacturing conditions and tempering of the alloy of the present invention are also not particularly restricted. Tempering suitable for the application may be selected under the usual production conditions. For example, the alloy may be T1 temper by a hot-processing finish; T6 temper by applying solution heat treatment and artificial aging; or T8 temper by applying solution heat treatment, cold-processing, and artificial aging. Further, tempers like T3, T8, T6, and T9, in which the alloy is subjected to cold-processing or artificial aging after solution heat treatment are also preferable, since chip splittability becomes better when the mechanical strength is greater.
In the present invention, the temperature of the material for forging is preferably 320 to 450xc2x0 C. and more preferably 350 to 420xc2x0 C., when the alloy material is processed by forging.
Cracks that are not found in the conventional alloys prepared by adding Pb and Bi are occurred in some cased in water-quenching after solution heat treatment carried out after forging when the alloy material prepared by adding Sn is subjected to hot forging. The present inventors found the reason to be as follows, through intensive studies. When the alloy is forged at a high temperature exceeding 450xc2x0 C., giant recrystallized crystalline grains are formed, and a large stress is applied to the recrystallized crystalline grain boundary by water-quenching applied after solution heat treatment. The total area of grain boundaries in the material having the giant recrystallization crystalline grains is so small that the stress applied on a unit area of the grain boundaries is increased, to readily cause cracks. Although the cracks are occurred in the conventional aluminum-based alloy material prepared by adding Pb and Bi when the further giant recrystallized crystalline grains are formed, the incidence of cracks is not as large as in the aluminum-based alloy material prepared by adding Sn, such as the alloy material of the present invention.
On the other hand, deformation resistance of the material increases when the temperature of the material is lowered during forging. It may be conjectured that the forging load may exceed the capacity of a press machine by the increase of deformation resistance. However, since the deformation resistance is small in the alloy of the present invention, as compared with the conventional aluminum alloy material prepared by adding Pb and Bi, low-temperature forging is possible. The forging load may be increased at a temperature lower than 320xc2x0 C., depending on the shape of the article to be obtained by forging. Lowering the temperature of the material during forging is advantageous with respect to energy cost.
The aluminum alloy of the present invention can be used, for example, for members or parts that are subjected to machining, such as cutting and drilling.
The aluminum alloy of the present invention has good cuttability that is equal or superior to the alloy prepared by adding Pb, by adding a prescribed amount of Sn and Bi, and adding Zn, even if Pb is not added, in the Alxe2x80x94Cu-series alloy.
According to the method of the present invention for producing a forged article, forging is possible at a lower temperature with a smaller load, to enable energy-saving forging while preventing cracks from occurring in the forging process (for example, in the water quenching after solution heat treatment after forging).
The present invention will be described in more detail based on examples given below, but the invention is not meant to be limited by these examples.